Measuring and ordering correct custom-length pushrods

John

Active Member
A friend came over to measure pushrods for a SBC going in my truck. He used a Comp Cams adjustable pushrod I bought for the job, one of the hydraulic lifters that will be used in the motor (Comp 812-16), and 12" digital calipers I have. I've never done this before but read up on it and watched several youtube videos just to learn what I could about what needed to be done to do this right. The intake is not on the motor yet, making this job a little easier. This is a shortblock I ordered with the heads installed but no oil in yet, just assembly lube.

So that said, using zero-lash method, after some adjusting, we got a great wear pattern centered on the tip of the valve stem and arrived at "the number." 7.996" if it matters. I'd already called Comp Cams Tech line once and was told the lifter I'm using pumps up .030". So before I spend $165 on custom pushrods, I called them back to walk through the numbers and make sure I'm placing the correct order.

So, to cut to the chase, I thought I needed to subtract .030 from 7.996 and order 7.966" length pushrods, and I'm calling them to confirm this. The tech I got (young buck, not that it matters) tells me No, I need to ADD .030 to the measurement.

I've read the link here: http://garage.grumpysperformance.co...-pushrods-and-check-info-you-might-need.5931/ and it's sub-links, admittedly I'm doing a lot of skimming because I'm looking for info on how to properly compensate for using a dry hydraulic lifter when measuring for pushrods.

So.. Is the young buck right? To my way of thinking, I'd end up installing pushrods that are too long that are going to be WAY too long when the lifters pump up. But I'm no engine builder and need some help with this. Thanks+++
 

Grumpy

The Grumpy Grease Monkey mechanical engineer.
Staff member
hydr1.png

hydr2.png


watch this video, it depicts the lifters movement as the cam lobe rotates under its base forcing it up as the lobes ramp, rotates under the lifter base,removing the clearance slack,
as it compresses the valve spring and forces the trapped oil, up the push rod and lifts the valve
If you are concerned with measuring the clearance in the hydraulic lifter seat when selecting and measuring the correct valve train geometry,
so you can order the correct length push rods...
I don,t think you have the correct idea as to how hydraulic lifters work,
yes it is possible for an engine with hydraulic lifters to be pushed too operate at a high enough rpm that the time required for the lifter seat to fully depress and all the oil too be forced up to the push rod/rockers , to be so short that the lifter pumps up and the valves will have less seat time, ( sometimes one of several factors, like the lifter leaving the cam lobes surface as the inertial loads exceed the valve springs ability to maintain lifter too lobe contact, referred too or contributing to what is commonly referred too as valve float) but that has ZERO to do with selecting push rod length or proper valve train geometry, (remember at 6000 rpm the valve is lifted off its seat 50 times PER SECOND)
hydrlifth.jpg


12cal.jpg


If you suspect a worn cam lobe, checking the cams lobe lift with a dial indicator on the valve spring retainer vs the other lobes would certainly provide useful related info.
knowing vs guessing helps in making decisions wisely
http://www.summitracing.com/parts/pro-66830/overview/
pro-66830_cp.jpg



https://www.harborfreight.com/multipositional-magnetic-base-with-fine-adjustment-5645.html

bv93fans.jpg

https://www.harborfreight.com/catalogsearch/result/index/?dir=asc&order=EAScore,f,EAFeatured+Weight,f,Sale+Rank,f&q=indicator+stand


rockeroilfeed.jpg

longslotz.jpg

check all valve train geometry and clearance on any engine you assemble or modify the valve train on.
bbcvtq5.jpg

bbcvtq6.jpg

prctool.png

now if your like me and your an old geezer you tend to adjust hydraulic lifters with the engine at idle and you back off the rocker until it clicks, slowly tighten it just to the point the clicking stops and then add 1/4 turn, and lock the rocker nut set screw.

dscn1098.jpg

rockadj.jpg


DSC00099.jpg

feeler_gauge2z.jpg

you can adjust solid flat tappet lifters in a vaguely similar way by inserting a proper thickness tappet feeler gauge between the rocker arm tip and valve tip,after loosening the rocker until there's more than enough lash clearance, too allow the tappet feeler gauge to slid in then slowly tighten the rocker nut to just the point where the clicking stops, remove the tappet feeler gauge and lock the nut on the stud at that point, you'll get a smooth rhythmic ticking which is exactly how a properly lashed solid lifter valve train sounds,


yodam.jpg

valvetip.jpg

13cal.jpg

http://www.racingsprings.com/

SOME ROLLER ROCKERS CAN AND DO BIND ON ROCKER STUDS, or rocker adjustment nuts, youll need to check carefully
rpo1x.JPG

some roller rocker too retainer combo clearance issues cause problems easily solved with beehive springs and smaller retainer diameters
beehivesprcl.jpg

for several years even stock BBC engines ,(the markVI and mark V) as opposed to the (mark IV earlier BBC engines)
also don,t use adjustable rocker arms if your running a stock cam and valve train with stock O.E.M. heads you probably can get by without them,
swap to a higher lift cam and a longer duration and aftermarket heads and better valve strings and in my opinion,
you would be very foolish to build and use a performance BBC engine without adjustable push rod guide plates
what you really should do is order these
Dart 27001230-4 - Dart Pushrod Guideplates

301-27001230-4.jpg



viewtopic.php?f=44&t=2839&p=7344&hilit=adjustable+guide#p7344

496bbcfgh.jpg

BEEHIVE SPRINGS GIVE A GOOD DEAL MORE ROCKER TO RETAINER CLEARANCE
http://www.summitracing.com/search/...d-length-checkers?autoview=SKU&ibanner=SREPD5
Proform Pushrod Length Checkers 66789 SBC 3/8" rocker studs

Proform Pushrod Length Checkers 66790 SBC 7/16" rocker studs

Proform Pushrod Length Checkers 66806 BBC 7/16" rocker studs
http://garage.grumpysperformance.com/index.php?threads/valve-train-clearances-and-problems.528/

http://garage.grumpysperformance.co...e-springs-and-setting-up-the-valve-train.181/

http://garage.grumpysperformance.com/index.php?threads/stock-gm-push-rod-length.3844/


http://garage.grumpysperformance.co...e-used-prw-stainless-steel-rocker-arms.14896/

http://garage.grumpysperformance.com/index.php?threads/rocker-push-rod-wear-issues.9815/

http://garage.grumpysperformance.co...1-6-1-ratio-rockers-and-the-pushrods-rub.198/


http://garage.grumpysperformance.co...mall-block-chevy-guide-plates.2839/#post-7344


http://garage.grumpysperformance.com/index.php?threads/decent-deal-on-these-push-rod-length-checker-tools.13735/#post-70650

http://garage.grumpysperformance.co...rockers-which-is-best-steel-or-aluminum.3124/


http://garage.grumpysperformance.com/index.php?threads/valve-springs.9613/

http://garage.grumpysperformance.co...lve-springs-loads-and-installed-height.10709/

http://garage.grumpysperformance.com/index.php?threads/press-in-vs-threaded-rocker-studs.2746/

http://garage.grumpysperformance.co...s-changing-rocker-ratios-and-the-effects.126/

http://garage.grumpysperformance.com/index.php?threads/understanding-valve-spring-bind-height-060-safety-margin.4957/
 
Last edited:

John

Active Member
Thanks Paul. I don't know where or when, but somehow I got the notion that when hydraulic lifters pump up the "cup" in the top of the lifter moved up in the bore. I don't mind my own ignorance but I'm a little irritated that Comp Cams tech line "aided and abetted". So if we can assume they were measured properly and the number is 7.996", then I can order a set of 8" pushrods and not bother with a custom order?
 

Grumpy

The Grumpy Grease Monkey mechanical engineer.
Staff member
if you measured correctly , yes purchasing a set of 8" push rods for that application, would be about ideal
have you used one of the push-rod length checker tools?
prctool.png

they might be a good cross check, before you order the push-rods.

it would take a bit more time but it would be cheaper in the long term.
to be sure you got it right than it would be to try to return push-rods

remember the tool works when the lifters on the cams base circle
(yes as simple as they are (PICTURE ABOVE) too use they tend to be rather accurate)

yes I use BOTH the push rod checker tools to get the quick check on length, and the adjustable length push-rods and a marker too method verify the correct length with a cross check by looking at the wear/sweep and location, on the valve tip
valvetip.jpg

http://garage.grumpysperformance.co...sh-rod-length-checker-tools.13735/#post-70650
index.php

some roller rocker too retainer combo clearance issues cause problems easily solved with beehive springs and smaller retainer diameters
beehivesprcl.jpg

for several years even stock BBC engines ,(the markVI and mark V) as opposed to the (mark IV earlier BBC engines)
also don,t use adjustable rocker arms if your running a stock cam and valve train with stock O.E.M. heads you probably can get by without them,
swap to a higher lift cam and a longer duration and aftermarket heads and better valve strings and in my opinion,
you would be very foolish to build and use a performance BBC engine without adjustable push rod guide plates
what you really should do is order these
Dart 27001230-4 - Dart Pushrod Guideplates

301-27001230-4.jpg

13cal.jpg


viewtopic.php?f=44&t=2839&p=7344&hilit=adjustable+guide#p7344


http://www.summitracing.com/search/...d-length-checkers?autoview=SKU&ibanner=SREPD5
Proform Pushrod Length Checkers 66789 SBC 3/8" rocker studs


Proform Pushrod Length Checkers 66790 SBC 7/16" rocker studs


heres a bit of useful related push rod length info (POSTED HERE) youll want to select the correct set or SETS for your shop

Big Block Chevy, Standard Length Big Block Intake 3/8" / .080" 8.275"
295-7941-8 Big Block Chevy, Standard Length Big Block Exhaust 3/8" / .080" 9.250"
295-7969-8 Big Block Chevy, Standard Big Block +.100" Long Intake 3/8" / .080" 8.375"
295-7979-8 Big Block Chevy, Standard Big Block +.100" Long Exhaust 3/8" / .080" 9.350"
295-7951-8 Big Block Chevy, Standard Length Big Block Tall Deck Intake 3/8" / .080" 8.675"
295-7961-8 Big Block Chevy, Standard Length Big Block Tall Deck Exhaust 3/8" / .080" 9.650"
295-7800 V8 396-454 Retro Fit Pushrod Set, Intake & Exhaust, 1965-Present
3/8" / .080"
3/8" / .080" 7.725 Int.
8.675 Exh

295-7913-16 Small Block Chevy, Standard Length Small Block Chevy 3/8" / .080" 7.800"
295-7984-16 Small Block Chevy, +.100" Long 3/8" / .080" 7.900"
295-7934-16 Big Block Ford, Standard Length Ford `72-'78 429-460 3/8" / .080" 8.550"
295-7951-16 Big Block Ford, Standard Length Ford `69-'71 429-460 3/8" / .080" 8.675"
295-7582-16 Oldsmobile, Std Length 455 5/16" 9.550"


youll want too verify the correct valve train geometry and push rod length, just to be sure its correct , on any engine with a new cam installed, never assume anything
but once you know for certain,
thread on adjusting valves

http://garage.grumpysperformance.com/index.php?threads/correctly-adjusting-valves.196/

btw
the quick and dirty version,, to getting a
hydraulic flat tappet chevy SBC or BBC engine, with a new cam installed and adjusted
stampedcvrockersa.jpg

rockadj.jpg


install all the rockers on the 16 individual rocker studs, so they just touch the push rods and valve stems with minimal slack,and are just loose enough that none bind
,
now,rotate engine about 45 degrees and and repeat,the process by tightening any individual rocker ,
that got looser, so they are just loose enough that none bind
rotate engine about 45 degrees and and repeat,tightening only the rockers that got looser ,
so they are just loose enough that none bind
while you, ignore the others, that will be tighter as the engines rotated,
do this enough times that the engines been through 720 degrees (start anywhere )and take the slack out of any loose rockers, repeat for 720 degrees,(twice around) then go back and give each rocker nut one turn OUT(LOOSER) and start the engine,(yeah it will be messy and noisy) and then go back and turn each rocker IN (TIGHTER) until it just quits clicking as that individual rocker cycles as the engine idles, then add pre-load,by turning the rocker in tighter plus 1/4 -1/3rd of a turn past that point


OR


Valve Adjustment: ENGINE OFF!

with #1 cylinder Intake Valve at full valve lift .... Adjust #6 Intake Valve
with #8 cylinder Intake Valve at full valve lift .... Adjust #5 Intake Valve
with #4 cylinder Intake Valve at full valve lift .... Adjust #7 Intake Valve
with #3 cylinder Intake Valve at full valve lift .... Adjust #2 Intake Valve
with #6 cylinder Intake Valve at full valve lift .... Adjust #1 Intake Valve
with #5 cylinder Intake Valve at full valve lift .... Adjust #8 Intake Valve
with #7 cylinder Intake Valve at full valve lift .... Adjust #4 Intake Valve
with #2 cylinder Intake Valve at full valve lift .... Adjust #3 Intake Valve

Exhaust Valve Adjustment: ENGINE OFF!

If you have noticed, this is the same procedure as the intake valves listed above, just that you are now adjusting the exhaust valves the same way.

with #1 cylinder Exhaust Valve at full valve lift .... Adjust #6 Exhaust Valve
with #8 cylinder Exhaust Valve at full valve lift .... Adjust #5 Exhaust Valve
with #4 cylinder Exhaust Valve at full valve lift .... Adjust #7 Exhaust Valve
with #3 cylinder Exhaust Valve at full valve lift .... Adjust #2 Exhaust Valve
with #6 cylinder Exhaust Valve at full valve lift .... Adjust #1 Exhaust Valve
with #5 cylinder Exhaust Valve at full valve lift .... Adjust #8 Exhaust Valve
with #7 cylinder Exhaust Valve at full valve lift .... Adjust #4 Exhaust Valve
with #2 cylinder Exhaust Valve at full valve lift .... Adjust #3 Exhaust Valve

http://garage.grumpysperformance.co...rect-custom-length-pushrods.14241/#post-72353

http://garage.grumpysperformance.com/index.php?threads/pushrod-length-tolerance.15189/#post-86918

http://garage.grumpysperformance.co...nd-check-info-you-might-need.5931/#post-18267

http://mantonpushrods.com/pushrod-info/determine-length/

https://www.enginelabs.com/engine-t...ing-valvetrain-geometry-and-getting-it-right/

https://www.hotrod.com/articles/how-to-measure-for-correct-length-pushrods/

https://www.hotrod.com/articles/setting-pushrod-length/

https://www.summitracing.com/parts/pro-66789

index.php


https://www.summitracing.com/parts/tfs-9501
tfs-9501_gv_xl.jpg

13cal.jpg




some time spent reading related links about your potential valve train issues could prevent lots of potential problems
http://garage.grumpysperformance.co...-pushrods-and-check-info-you-might-need.5931/
http://garage.grumpysperformance.co...rect-custom-length-pushrods.14241/#post-72353
http://garage.grumpysperformance.co...-rockers-and-the-pushrods-rub.198/#post-46839
http://garage.grumpysperformance.com/index.php?threads/press-in-vs-threaded-rocker-studs.2746/
http://garage.grumpysperformance.co...s-tool-swapping-to-1-6-1-ratio-rockers.14761/
http://garage.grumpysperformance.co...rdering-correct-custom-length-pushrods.14241/
http://garage.grumpysperformance.co...ange-in-valve-spring-iinstalled-height.12791/
http://garage.grumpysperformance.co...1-6-1-ratio-rockers-and-the-pushrods-rub.198/
 
Last edited:

John

Active Member
Thanks. That's an easy and cheap way to verify. I just ordered one with some other stuff I needed. I'll use it to double-check before ordering the pushrods.
 

Grumpy

The Grumpy Grease Monkey mechanical engineer.
Staff member
On the plus side, this thread,helped me in a small way,
you had me checking my valve train precision tool section of my tool box,
and when I realized I had foolishly loaned out my BBC check tool, and it never got returned,
so I ordered a new one, from summit... as I damn sure don,t want to rely exclusively on the adjustable push-rods
https://www.summitracing.com/parts/pro-66806/overview/
tippattern.jpg

tappet%20adjustment_zps8vi9yxmu.jpg

Ive got a drawer full of related valve train geometry and push-rod length checking tools and assorted valve spring and degree wheel, tools simply because getting the rocker geometry wrong tends to cause expensive parts failures,
http://garage.grumpysperformance.co...sh-rod-length-checker-tools.13735/#post-70650
while this may sound like the cost to get the rocker geometry correct,
are a bit expensive its really not a bad price for a selection of adjustable push-rods,
that may prevent much more expensive issues if your building an engine
I already have several but they are at least 40 years old and I figured its about time to get a few extras
maybe its just me, but I like to verify all my engine clearances and rocker geometry , as it reduces potential problems


related threads and linked info
http://garage.grumpysperformance.co...ng-cam-and-shifting-the-lca.10553/#post-44949

http://garage.grumpysperformance.co...et-it-to-last-cam-install-info.90/#post-57942

http://garage.grumpysperformance.com/index.php?threads/cam-degreeing.9010/#post-35474

http://garage.grumpysperformance.com/index.php?threads/degree-in-that-cam-correctly.27/#post-49079

http://garage.grumpysperformance.com/index.php?threads/cam-degree-equipment-tools.1759/#post-4435

http://garage.grumpysperformance.co...ting-up-the-valve-train.181/page-2#post-54091

http://garage.grumpysperformance.com/index.php?threads/precision-measuring-tools.1390/#post-52466

http://garage.grumpysperformance.com/index.php?threads/rhodes-lifters.1552/#post-6067

http://garage.grumpysperformance.co...train-clearances-and-problems.528/#post-57678

http://garage.grumpysperformance.co...t-compressed-when-installed.11356/#post-51869

 
Last edited:

Loves302Chevy

"One test is worth a thousand expert opinions."
Also, if you must, it is better to have the pushrod slightly shorter than ideal.
Think about it, the spring pressures are lower on the valve tip at minimum lift.
At max sweep (higher spring pressure), you would rather have the rocker pushing down
on the center of the valve stem for less side loading of the valve guide.
 

Grumpy

The Grumpy Grease Monkey mechanical engineer.
Staff member
if your within about .030 of the ideal, push-rod length, the difference, in valve train geometry and stress,
with the push -rods a bit longer or shorter, is negligible but you should try hard to be closer than .050 to the ideal length,
yes that means if your within .050 youll be reasonably ok.
 
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